queue::front
Returns a reference to the first element at the front of the queue.
reference front( );
const_reference front( ) const;
Return Value
The first element of the queue. If the queue is empty, the return value is undefined.
Remarks
If the return value of front is assigned to a const_reference, the queue object cannot be modified. If the return value of front is assigned to a reference, the queue object can be modified.
The member function returns a reference to the first element of the controlled sequence, which must be nonempty.
When compiling with _SECURE_SCL 1, a runtime error will occur if you attempt to access an element in an empty queue. See Checked Iterators for more information.
Example
// queue_front.cpp
// compile with: /EHsc
#include <queue>
#include <iostream>
int main() {
using namespace std;
queue <int> q1;
q1.push( 10 );
q1.push( 20 );
q1.push( 30 );
queue <int>::size_type i;
i = q1.size( );
cout << "The queue length is " << i << "." << endl;
int& ii = q1.back( );
int& iii = q1.front( );
cout << "The integer at the back of queue q1 is " << ii
<< "." << endl;
cout << "The integer at the front of queue q1 is " << iii
<< "." << endl;
}
Output
The queue length is 3. The integer at the back of queue q1 is 30. The integer at the front of queue q1 is 10.
Requirements
Header: <queue>
Namespace: std